The present invention relates to an apparatus for processing waste. In particular, the present invention is directed to an apparatus adapted for processing liquid waste in a plasma torch based waste processing plant.
The processing of waste including municipal waste, medical waste, toxic and radioactive waste by means of plasma-torch based waste processing plants is well known. Referring to FIG. 1, a typical prior art plasma-based processing plant (1) comprises a processing chamber (10) typically in the form of a vertical shaft, in which solid or mixed (i.e., solid plus liquid and/or semiliquid and/or gaseous) waste (20) is introduced at the upper end thereof via a air lock arrangement (30). One or a plurality of plasma torches (40) at the lower end of the chamber (10) heats the column (35) of waste in the chamber (10), converting the waste into gases that are channeled off via outlet (50), and a liquid material (38) (typically molten metals and/or slag) which is periodically collected at the lower end of the chamber (10) via reservoir (60). Oxidising fluid, such as air, oxygen or steam (70) may be provided at the lower end of the chamber (10) to convert carbon, produced in the processing of organic waste, into useful gases such as CO and H2, for example. A similar arrangement for dealing with solid waste is described in U.S. Pat No. 5,143,000, the contents of which are incorporated herein by reference thereto.
While suitable for dealing with solid waste, this type of processing plant is generally unsuitable for dealing with liquid waste, in particular liquid organic waste and other liquid waste which are volatile in the lower to mid temperature range, i.e., between less than 100xc2x0 C. to about 500xc2x0 C. Such liquid waste, when fed to the chamber (10) via the upper air lock arrangement (30) tends to be vaporised well before reaching the lower, high-temperature portions of the chamber (10). Thus, such liquid waste is converted to gaseous waste which subsequently is channeled off, substantially unchanged chemically, via gas output (50), rather than processed and converted by the plasma torches (40). Accordingly, such liquid waste still needs to be further processed downstream in specialised incinerators or other processing facilities.
Furthermore, even when dealing with solid waste, particulate matter and also pitch tend to be entrained with product gases produced in the high temperature conversion process, and are removed from the chamber (10) via gas outlet (50). Such particulate matter may include other organic matter which is removed from the chamber (10) before it has been fully converted by the hot gases generated by the plasma torches. While a scrubber system may be used, in particular a wet scrubbing system, for cleaning the product gases, the particulate matter and the pitch nevertheless need to be further treated.
A number of devices have been proposed for dealing with liquid-type waste. For example, in U.S. Pat. No. 4,989,522, mixed waste is separated into solid waste and liquid waste, the latter being fed to the converting chamber via a separate inlet at the top of the chamber, leading to similar problems of vaporisation, as described above.
In U.S. Pat. No. 5,809,911, a complex multi-zone waste processing system includes a feed subsystem for providing liquid waste to a first reactor. The feed subsystem is located below the plasma torch, and thus the liquid waste is entrained with the plasma jet towards the bed of molten slag material that collects at the bottom of the chamber. The great disadvantage of this arrangement is that the liquid waste effectively cools the slag, leading to crystatisation and partial solidification of the same, which causes complications in removing the solid conversion products from the chamber.
In U.S. Pat. No. 5,637,127, a method for dealing with liquid waste or finely divided solid waste includes mixing the waste with finely divided glassformers and injected directly into a melting duct or tuyere, where it is mixed with the plume of a non-transferred plasma torch prior to being introduced into the chamber proper. The waste-transformer mixture is converted into a fully vitrified glass product, which may be collected from the bottom of the chamber. Thus, this system cannot deal also with regular solid waste, and in any case the liquid waste needs to be preprocessed with the glassformers. Furthermore, the system is designed particularly for inorganic waste, and is not as suitable for dealing with organic liquid waste, in which the conversion process results in gaseous rather than vitrified products.
In U.S. Pat. No. 4,886,001, waste is mixed with water/methanol solvent, and the mixture is injected into a manifold concentric with a plasma torch, and mixed with air prior to encountering the plume of the plasma torch. The addition of water to the waste increases the feed throughput rate of the apparatus, as compared with prior systems which use an expensive MEK/methanol mixture rather than water/methanol. Thus, this system is not suitable for dealing also with solid waste directly, and the preprocessing of the waste with water/methanol results in added complexity and costs.
In U.S. Pat. No. 5,363,781, a device for treatment of liquid and gas waste is described, in which a plasma torch comprises integral tubes or the like for transporting the waste directly to the plasma plume via nozzles disposed at the ends of the tubes. The device is directed to small-scale waste disposal operations, and cannot also deal with solid waste.
Furthermore, none of the above patents, the contents of which are incorporated herein by reference thereto, disclose nor suggest how to deal with particulate matter or pitch entrained by the gasses produced in a regular plasma torch based waste conversion chamber and channeled away therefrom.
It is therefore an aim of the present invention to provide a device and method for dealing with liquid waste which overcomes the limitations of prior art devices and methods.
It is another aim of the present invention to provide such a device that may be incorporated into a solid waste processing apparatus.
It is another aim of the present invention to provide a device for processing liquid waste directly in a plasma-torch type processing apparatus.
It is another aim of the present invention to provide such a device that may also be used for treating particulate matter and pitch previously removed from the plasma torch based processing apparatus.
It is another aim of the present invention to provide such a device that is relatively simple mechanically and thus economic to produce as well as to maintain.
It is another aim of the present invention to provide such a device that incorporates a liquid feed system for feeding liquid waste directly into such an apparatus without the need for preprocessing the waste, in particular such preprocessing in which solvents or other materials are added to the waste.
It is another aim of the present invention to provide such a device for processing liquid waste incorporated as an integral part of a plasma-torch based type mixed waste converter.
It is also an aim of the present invention to provide such a device for processing liquid waste that is readily retrofittable with respect to at least some existing plasma-based solid waste and/or mixed waste converters.
The present invention achieves these and other aims by providing a liquid waste feeding system having an inlet to a plasma torch based waste processing chamber, the liquid inlet being disposed intermediate the primary plasma torch arrangement at the bottom end of the chamber and the top of the waste column within the chamber, in particular the gas products outlet. Further, the liquid inlet is disposed within the chamber such that liquid waste flowing from the inlet into the chamber is directed at a high temperature zone of waste column, and the liquid inlet is typically associated with a hot gas jet means. The hot gas jet means that provides the required high temperature zone may comprise one or more secondary plasma torches configured to provide hot gas jets into the liquid discharge zone of the inlet. Alternatively, the hot gas jet may be provided by the primary plasma torches, in which case the liquid inlet is disposed within a predetermined area close to and above at least one of the primary plasma torches.
The present invention relates to a device for converting liquid waste within a waste converting apparatus, the waste converting apparatus having a waste converting chamber adapted for accommodating a column of waste, at least one first plasma torch means for generating a hot gas jet at an output end thereof and for directing said jet towards a bottom longitudinal part of the chamber and at least one gas outlet means at an upper longitudinal part of the chamber, said device comprising:
at least one liquid waste inlet for providing liquid communication between said chamber and a supply of liquid waste, said at least one liquid inlet being longitudinally disposed intermediate said output end of said at least one first plasma torch means and said at least one gas outlet means, wherein said liquid inlet is associated with at least one plasma torch means such that during operation of said device liquid waste flowing from the inlet into said chamber is directed at a high temperature zone provided by the at least one plasma torch means that is associated with said at least one liquid inlet.
In a first embodiment, the at least one plasma torch means that is associated with said at least one liquid inlet is at least one of said first plasma torch means. In this embodiment, the at least one liquid inlet is located within a predetermined arc above said at least one first plasma torch means in close proximity thereto. The arc is typically about xc2x130xc2x0 from a centerline of said at least one plasma torch means.
In a second embodiment, the at least one plasma torch means that is associated with said at least one liquid inlet comprises a corresponding at least one second plasma torch means. In this embodiment, the at least one liquid inlet and said at least one second plasma torch means may be disposed in a mixing chamber in communication with said chamber. Alternatively, the at least one liquid inlet and said one second plasma torch means are located within said chamber, wherein said at least one liquid inlet and said at least one plasma torch means are preferably coplanar, the plane containing said at least one liquid inlet and said at least one second plasma torch means being preferably substantially perpendicular to a longitudinal axis of said chamber.
The present invention is also directed to an apparatus for converting waste comprising:
a waste converting chamber adapted for accommodating a column of waste;
at least one first plasma torch means for generating a hot gas jet at an output end thereof and for directing said jet towards a bottom longitudinal part of the chamber;
at least one gas outlet means at an upper longitudinal part of the chamber,
said device fisher comprising a device for converting liquid waste, said device comprising:
at least one liquid waste inlet for providing liquid communication between said chamber and a supply of liquid waste, said at least one liquid inlet being longitudinally disposed intermediate said at least one first plasma torch means and said at least one gas outlet means, wherein said liquid inlet is associated with at least one plasma torch means such that during operation of said device liquid waste flowing from the inlet into said chamber is directed at a high temperature zone provided by the at least one plasma torch means that is associated with said at least one liquid inlet.
In the first embodiment, the at least one plasma torch means that is associated with said at least one liquid inlet is at least one of said first plasma torch means, and the at least one liquid inlet is located within a predetermined arc above said at least one first plasma torch means in close proximity thereto. Typically, the arc is about xc2x130xc2x0 from a centerline of said at least one plasma torch means.
In a second embodiment, the at least one plasma torch means that is associated with said at least one liquid inlet comprises a corresponding at least one second plasma torch means. In this embodiment, the at least one liquid inlet and said at least one second plasma torch means may be disposed in a mixing chamber in communication with said chamber. Alternatively, the at least one liquid inlet and said one second plasma torch means are located within said chamber, and the at least one liquid inlet and said at least one plasma torch means may be coplanar, wherein the plane of containing said at least one liquid inlet and said at least one second plasma torch means is preferably substantially perpendicular to a longitudinal axis of said chamber.
The apparatus optionally further comprises waste input means associated with said upper part of said chamber. The waste input means may comprise an air lock means comprising a loading chamber for isolating a predetermined quantity of said waste sequentially from an inside of said chamber and from an outside of said chamber. Optionally, the waste input means further comprises suitable disinfecting means for selectively delivering a quantity of suitable disinfectant to at least an outer portion of said air lock means.
The apparatus optionally further comprises a suitable collection means for collecting molten products during operation of said apparatus. The apparatus may comprise at least one outlet port for delivering molten products from said collection means to an outside of said apparatus.
The at least one gas outlet means may be operatively connected to a scrubber means for removing at least one of particulate matter, liquid matter or unwanted gases entrained with product gas stream leaving said chamber via said at least one gas outlet means. Optionally, the scrubber means comprises a reservoir means for collecting at least one of said particulate matter or liquid matter removed by said scrubber. The reservoir means may be operatively connected to said at least one liquid waste inlet means for redirecting any one of said particulate matter of liquid matter in said reservoir means to said chamber.
The apparatus may be adapted for accommodating solid waste and/or liquid waste in said chamber. The liquid waste may comprise at least one of volatile liquid waste or organic liquid waste.